The proposed research is designed to yield a better understanding of the function of ras proteins and to make functional comparisons with the related G proteins that are involved in signal transduction across the plasma membrane. The approach will be based on the unique properties of a newly characterized ras mutant (17asn rasH) that has greater than 1,000 fold higher affinity for GDP than GTP and whose expression in NIH cells appears to block NIH cell growth by interfering with the normal ras pathway. Biochemical and genetic techniques will be used to exploit these properties in the identification of regulatory proteins whose function is dependent upon ras and factors that regulate ras function. Finally, because the amino acid altered in this ras mutant is conserved in all alpha-subunits of G proteins, the effect of analogous mutations in Gs alpha, the protein that couples stimulatory hormone receptors to adenylate cyclase will be assessed. In this well characterized system, the mechanism responsible for altered phenotypes induced by these mutations will be studied.